At present, thermoplastic resins such as propylene resins, styrene resins, acrylonitrile/butadiene/styrene (ABS) resins, and high-impact polystyrene resins having improved impact resistance are generally used for housings of TVs and PC monitors and those for various home electric appliances These are used with additive components incorporated for the purpose of imparting various functions to the resins. For example, as thermoplastic resins have high combustibility by themselves, the resins are mixed with flame retardants and flame retardant auxiliaries in a proportion of about 10 to 25% by weight from the viewpoint of preventing the spread of fire during the fire. In particular, bromine-based flame retardants have a high flame retarding effect on various resins and have a low price, so that they have been globally used.
The bromine-based flame retardants have excellent flame retardancy to aromatic resins represented by styrenic resins and have been used in large quantities for various housings and component materials in home electric appliances. Hence, resin compositions containing the bromine-based flame retardants are discarded in large quantities when these home electric appliances are scrapped.
Generally, in the methods of treating resin wastes, incineration and landfill have been mainly employed and only a part of them is recycled through heating/melting or the like. It is desired to dispose of waste plastics by incineration considering shortages of landfill site. However, the resin compositions containing flame retardancy find difficulty in incineration due to the high degree of flame retardancy imparted thereto, finding difficulty in disposing.
In addition, as awareness to environmental issues is raised, the harmful effect of halogenated organic substances on environment is pointed out and the use of the halogenated organic substances is being restricted. At present, each of the users is under review of switching the halogenated flame retardants to the flame retardants containing no halogenated organic substances such as phosphorus-based compounds. However, the phosphorus-based compounds have less capability of imparting flame retardancy compared to the halogenated organic substances, so that the present situation is that the switching from the halogenated organic substances almost stops.
Further, in recent years, the reuse of the resources derived from petroleum chemistry is strongly requested and the establishment of the methods of resin waste disposal and recycling has become an important issue. Particularly, the Electric Appliance Recycling Law that has come into effect since April 2001 requests suitable recycling treatment on TV sets, refrigerators, air conditioners, and washing machines.
For the time being the target of the recycling rate is about 50 to 60%, which may be met by the efforts for promoting the recycling of glass and metal that occupy relatively large proportion by weight in each of the products. However, as the target is anticipated to become higher in future, the establishment of the resin recycling method is desired.
Various studies have been carried out on a method of treating a resin composition containing a flame retardant. However, these studies mainly include acid treatment (Japanese Patent Laid-Open No. 6-157812) or high temperature treatment (Japanese Patent Laid-Open No. 8-299759, Japanese Patent Laid-Open No. 9-262565, and Japanese Patent Laid-Open No. 2000-198874). They mainly include the thermal cycle treatment in which a resin and a flame retardant are completely decomposed. Almost no efforts with the objective of material recycling of resins are found. Japanese Patent Laid-Open No. 10-195234 proposes a method of separating a flame retardant from a resin by modifying the resin. This method considers the use of the resin to other applications by functionalizing it. However, we think that the establishment of a recycling method mainly of recycling the resin to general-purpose applications is urgent.